Crystalline silicon photovoltaic modules typically comprise a plurality of solar cells laminated between a first layer and a second layer of ethylene-vinyl acetate (EVA) polymeric material, a glass substrate adhered to the first layer of polymeric material, and a Tedlar.RTM.-polyester-Tedlar.RTM. polymeric backing sheet adhered to the second layer of polymeric material. Lead soldered electrical ribbon is used to interconnect the solar cells of the module. A power collection system is used to convey power generated from the module to other components.
A typical solar cell comprises an expensive high purity silicon wafer having a first side doped with boron, a second side doped with phosphorus, and silver contact grids on both sides. The solar cells accounts for about fifty percent of the total cost of the raw materials of a crystalline silicon photovoltaic module. A crystalline silicon photovoltaic module could theoretically be used for many years without suffering any loss in efficiency since they do not experience any photodegradatation. However, a lamination defect, broken or chipped glass substrate, or failure of the power collection system usually results after a period of time rendering the entire module inoperative even though the relatively expensive solar cells are still operable. Moreover, lead is a potentially hazardous material, and as such, requires disposal considerations. Until now, there has been no acceptable method for recycling silicon photovoltaic modules to recover the solar cells, the lead and other module components from the modules.
Some unsuccessful attempts have been made to recover silicon wafers from silicon photovoltaic modules in the past. One such attempt employed a nitric acid etching system to free the silicon wafer from the EVA polymeric layers. While this method resulted in the recovery of intact silicon wafers, the silver cell contacts were completely etched from the silicon wafer, rendering the silicon wafer inoperable for use in a crystalline silicon photovoltaic module without reapplying silver cell contacts to the silicon wafer. Additionally, this nitric acid etching system also produced undesirable NO.sub.x gases and a contaminated waste acid stream. Another such attempt to recover silicon wafers from silicon photovoltaic modules involved thermal decomposition, which proved to be unsuccessful because of carbonization of the EVA polymer at 200.degree. C. in air.
Accordingly, it would be desirable to be able to recycle silicon photovoltaic modules to recover solar cells, lead and other module components without creating any undesirable gases. Moreover, it would be further desirable to be able to recover whole solar cells (i.e., silicon wafers still having their silver contact grids intact so that the solar cells could be reused to make other crystalline silicon photovoltaic modules without requiring reprocessing of the silicon wafers to apply the silver contact grids.